Dry wells are vertical infiltration systems to which roof or parking lot runoff is directed. Formal dry wells consist of excavations to an appropriate depth and width in which concrete dry well rings are installed. Dry well rings are concrete rings of varying diameters and heights that have perforation or holes to allow water to pass through to the surrounding soils. Water is routed to a dry well through pipes from downspouts or catch basins. The size of a dry well, like all infiltration systems, is determined by collection area and soil infiltration rates.
In the Portland Metro area, soil conditions vary considerably. Some areas are appropriate for dry wells and some are not. Generally speaking, most of NE and North Portland are appropriate for dry wells, as is souther Clark County. Some other locations can use dry wells or other (link) infiltration systems, but may require larger sizing.
Dry wells themselves are constructed by excavating a pit or hole to the appropriate depth. The hole is then lined with filter fabric to prevent migration of soil into the dry well. The dry well rings are then set in place. You could have 2 4′ diameter rings 4′ tall stacked on top of each other. A lid is placed on top of the rings, the pipe is routed into the dry well and drain rock is placed between the filter fabric and the outside of the dry well rings. The top of the dry well is typically 2′ or so below ground level. Soil is then backfilled over the dry well. Dry wells, (except in public streets) typically do not have access.
Drainage Masters can evaluate your drainage and soil conditions and design a system appropriate to you particular location.
Call or e-mail firstname.lastname@example.org Drainage Masters to arrange an appointment for a free evaluation and estimate